fix: make dogpile.cache.memory preserve its init parameters

Make the `MemoryBackend` behave like the others, and stop removing
keys from the initialization dict.

Fixes: Issue #273

Author: 0xDEC0DE

dogpile/cache/backends/memory.py

@@ -50,7 +50,7 @@ class MemoryBackend(CacheBackend):
     """
 
     def __init__(self, arguments):
-        self._cache = arguments.pop("cache_dict", {})
+        self._cache = arguments.get("cache_dict", {})
 
     def get(self, key):
         return self._cache.get(key, NO_VALUE)

dogpile/testing/fixtures.py

@@ -32,7 +32,14 @@ def setup_class(cls):
         backend_cls = _backend_loader.load(cls.backend)
         try:
             arguments = cls.config_args.get("arguments", {})
+            stashed = arguments.copy()
             backend = backend_cls(arguments)
+            # Fail the test if the parameters have been altered by the backend setup;
+            # the test results in such cases should be considered suspect
+            if arguments != stashed:
+                raise ValueError(
+                    f"Backend setup failure, test parameters have been altered: {arguments} != {stashed}"
+                )
         except ImportError:
             pytest.skip("Backend %s not installed" % cls.backend)
         cls._check_backend_available(backend)

tests/cache/test_memory_backend.py

@@ -4,6 +4,7 @@
 
 class MemoryBackendTest(_GenericBackendTestSuite):
     backend = "dogpile.cache.memory"
+    config_args = {"arguments": {"cache_dict": {"cache": "warm"}}}
 
 
 class MemoryBackendSerializerTest(